1. Field of the Invention
The present invention relates to a toroidal type continuously variable transmission which is used as, e.g., a transmission for a vehicle.
2. Related Background Art
The use, as a transmission for a vehicle, of a toroidal type continuously variable transmission shown in FIGS. 13 and 14 has been studied. In this toroidal type continuously variable transmission, as disclosed in, e.g., Japanese Laid-Open Utility Model Application No. 62-71465, an input-side disk 2 is supported to be concentrical with an input shaft 1 as an input member, and an output-side disk 4 is fixed to the end portion of an output shaft 3 as an output member. Trunnions 6 are swingable about pivot shafts 5 located at twisted positions with respect to the input shaft 1 and the output shaft 3, and are arranged on the inner surface of a casing which stores the toroidal type continuously variable transmission, or on a support bracket provided in the casing.
The pivot shafts 5 are provided to the outer surfaces of the two end portions of each trunnion 6. The proximal end portion of each displacement shaft 7 is supported by the central portion of a trunnion 6. When each trunnion 6 is swung about the pivot shafts 5, the inclination angle of each displacement shaft 7 can be freely adjusted. The displacement shaft 7 supported by each trunnion 6 rotatably supports a power roller 8. The power rollers 8 are clamped between the two, i.e., input- and output-side disks 2 and 4.
Opposing inner surfaces 2a and 4a of the input- and output-side disks 2 and 4 have arcuate recessed surface sections having the pivot shafts 5 as the centers. Circumferential surfaces 8a of the power rollers 8 which are formed to have spherical projecting surface sections are respectively in contact with the inner surfaces 2a and 4a.
A loading cam type compression device 9 is provided between the input shaft 1 and the input-side disk 2, and elastically presses the input-side disk 2 toward the output-side disk 4. The compression device 9 is constituted by a cam disk 10 which rotates together with the input shaft 1, and a plurality of (e.g., four) rollers 12 held by a holder 11. A cam surface 13 as a recessed/projecting surface extending across the circumferential direction is formed on one surface (the left surface in FIGS. 13 and 14) of the cam disk 10, and a similar cam surface 14 is formed on the outer surface (the right surface in FIGS. 13 and 14) of the input-side disk 2. The plurality of rollers 12 are rotatably supported to have, as the center, an axis in the radial direction with respect to the center of the input shaft 1.
In a use of the toroidal type continuously variable transmission with the above-mentioned structure, when the cam disk 10 is rotated upon rotation of the input shaft 1, the plurality of rollers 12 are pressed against the cam surface 14 formed on the outer surface of the input-side disk 2 by the cam surface 13. As a result, the input-side disk 2 is pressed against the plurality of power rollers 8, and at the same time, the input-side disk 2 is rotated upon meshing between the pair of cam surfaces 13 and 14 and the plurality of rollers 12. The rotation of the input-side disk 2 is transmitted to the output-side disk 4 via the plurality of power rollers 8, and the output shaft 3 fixed to the output-side disk 4 is rotated.
When the rotational speeds of the input and output shafts 1 and 3 are to be changed, e.g., when a deceleration is to be performed between the input and output shafts 1 and 3, the trunnions 6 are swung about the pivot shafts 5 to incline the displacement shafts 7, so that the circumferential surfaces 8a of the power rollers 8 contact portions, near the center, of the inner surface 2a of the input-side disk 2 and portions, near the outer periphery, of the inner surface 4a of the output-side disk 4, as shown in FIG. 13.
On the contrary, when an acceleration is to be performed, the trunnions 6 are swung to incline the displacement shafts 7, so that the circumferential surfaces 8a of the power rollers 8 contact portions, near the outer periphery, of the inner surface 2a of the input-side disk 2 and portions, near the center, of the inner surface 4a of the output-side disk 4, as shown in FIG. 14. When the inclination angle of the displacement shafts 7 is set to be an intermediate angle between FIGS. 13 and 14, an intermediate transmission ratio can be obtained between the input and output shafts 1 and 3.
FIG. 15 shows a toroidal type continuously variable transmission described in the microfiche film of Japanese Utility Model Application No. 61-87523 (Japanese Laid-Open Utility Model Application No. 62-199557), and shows a structure applied to a transmission for a vehicle. The rotation of a crankshaft of an engine is transmitted to an input shaft 16 via a clutch 15, thereby rotating the cam disk 10, which is spline-engaged with the middle portion of the input shaft 16. Upon operation of the compression device 9 including this cam disk 10, the input-side disk 2 is rotated while being pressed toward the output-side disk 4 (leftward in FIG. 15). The rotation of the input-side disk 2 is transmitted to the output-side disk 4 via the power rollers 8.
The output-side disk 4 is supported by a needle bearing 17 at a portion around the input shaft 16, and a cylindrical output shaft 29 formed integrally with the output-side disk 4 is supported by an angular type ball bearing 19 at the inner side of a housing 18. On the other hand, one end (the right end in FIG. 15) of the input shaft 16 is rotatably supported by a rolling bearing 20 at the inner side of the housing 18, and the other end thereof is rotatably supported by an angular type ball bearing 21 at the inner side of the housing 18.
A transmission gear 24 obtained by integrating a driving forward gear 22 and a driving backward gear 23 is spline-engaged with the outer circumferential surface of the output shaft 29. When a vehicle is to be driven forward, the transmission gear 24 is moved to the right to cause the drive-side forward gear 22 to directly mesh with a driven forward gear 26 provided at the middle portion of a pickup shaft 25; when a vehicle is to be driven backward, the transmission gear 24 is moved to the left to cause the driving backward gear 23 to mesh with a driven backward gear 27 fixed to the middle portion of the pickup shaft 25 via an intermediate gear (not shown).
In a use of the toroidal type continuously variable transmission with the above-mentioned structure, when the input shaft 16 is rotated by the engine via the clutch 15, and the transmission gear 24 is moved in a proper direction, the pickup shaft 25 can be rotated in an arbitrary direction. When the trunnions 6 are swung to change the contact positions between the circumferential surfaces 8a of the power rollers 8 and the inner surfaces 2a and 4a of the input- and output-side disks 2 and 4, the rotational speed ratio between the input shaft 16 and the pickup shaft 25 can be changed.
When the above-mentioned toroidal type continuously variable transmission is driven, the input-side disk 2 is pressed toward the output-side disk 4 upon operation of the compression device 9. As a result, a thrust load in the right direction in FIG. 15 acts, as a counterforce based on the pressing force, on the input shaft 16, which supports the cam disk 10 of the compression device 9. This thrust load is received by the ball bearing 21 via a nut 28 threadably engaged with the end portion of the input shaft 16. Also, a thrust load in the left direction in FIG. 15 acts on the output shaft 29 via the input- and output-side disks 2 and 4 and the power rollers 8 upon operation of the compression device 9. This thrust load is received by the ball bearing 19.
Note that FIG. 15 also illustrates an engine brake clutch 30 and a direct coupling clutch 31. However, since the structures and operations of these clutches are well known, a detailed description thereof will be omitted.
In the above-mentioned conventional structure shown in FIG. 15, the thrust loads in the opposing directions, which are generated upon operation of the compression device 9 in a driving state of the transmission, are independently received by the two ball bearings 19 and 21. Therefore, torque losses at portions of the ball bearings 19 and 21 based on the thrust loads are generated independently from each other.
The thrust loads are considerably large, and hence, the torque losses at the portions of the ball bearings 19 and 21 are also considerably large. Therefore, when the torque losses are independently generated at two positions, a loss of the toroidal type continuously variable transmission as a whole becomes considerably large, resulting in poor efficiency of the overall toroidal type continuously variable transmission.
Furthermore, in the conventional structure shown in FIG. 15, the thrust load transmitted from the output-side disk 4 to the output shaft 29 is transmitted to an inner ring 19a of the ball bearing 19 via a stop ring 133. Therefore, the stop ring 133 receives a considerably large thrust load upon operation of the toroidal type continuously variable transmission. However, it is difficult to assure high reliability and durability of the stop ring 133, and a demand has arisen for improving the structure.
Moreover, in the conventional structure shown in FIG. 15, when the cam disk 10 is pressed rightward upon operation of the compression device 9, and the rightward thrust load acts on the input shaft 16, the input shaft 16 is displaced to the right while compressing a coned disk spring 134 between a sleeve 130 and the nut 28. In this case, the outer surface of the distal end portion of the input shaft 16 is in sliding frictional contact with the inner surface of the sleeve 130. In the conventional structure, due to the sliding frictional contact between these two surfaces, a frictional force generated between the two surfaces becomes large, and a power loss inside the toroidal type continuously variable transmission increases accordingly.